I have deleted this one mailbox over and over but next time I start up Poco it's back. I delete mailboxes often, due to my eBay sales, but this is the first time I've had this problem.
Any clues please?

I should add that it, in itself, is now empty.
I've tried several more times since first posting, it STILL comes back!!!
It may sound daft but I even tried deleting my back files, deleting the mailbox and then re-backing up. It's still there.